1. Field of the Invention
This invention relates generally to radio frequency (RF) communication and more particularly to a multilayer integrated circuit for RF communication and methods for assembly thereof.
2. Description of the Background Art
Cell phone manufacturers are under competitive pressure to make cell phones smaller, less costly, more power efficient, and more sophisticated by adding new functional capabilities. Accordingly, designers may focus on reducing the size and cost of RF modules. An RF module of a typical handset includes the electronic circuitry for receiving, processing, and transmitting RF signals. Typically, the RF module consists of a radio frequency integrated circuit (RFIC) and passive electronic components. For example, the RFIC may include a voltage controlled oscillator, a low noise amplifier, a filter, a mixer, and an antenna. The passive electronic components include resistors, capacitors, and inductors.
In general, the passive components are not integrated with the RFIC, and consequently consume large areas of the RF module. For example, in a conventional RF module, a spiral inductor is a coil wound several times within a defined area on a single plane of the RF module. Since the spiral inductor has an inductance value proportional to various physical dimensions including the length of the coil and the number of windings, the inductor may consume a large percentage of costly RF module real estate.
FIG. 1 shows a conventional RF module 100 of the prior art. The conventional RF module 100 includes a plurality of RFICs 110, 120, and 130 mounted on a lead frame 105. The RFICs 110, 120, and 130 are electrically connected to a plurality of lead frame inductors 140, 150, and 160 through bonding wires 170. The lead frame inductors 140, 150, and 160 are formed of the same material as that of the lead frame 105 for impedance matching to the RFICs 110, 120, and 130. According to other embodiments of the prior art, the inductors 140, 150, and 160 may be configured on printed circuit boards (not shown), and electrically connected to the RFICs 110, 120, and 130 via the bonding wires 170. Size and configuration of the conventional RF module 100 is determined to a large extent by the modular space occupied by the lead frame inductors 140, 150, and 160. The constraint placed upon the size and configuration of the RF module 100 by the lead frame inductors 140, 150, and 160 is disadvantageous to design engineers for developing smaller, lower cost handsets with efficient heat dissipation properties.
FIG. 2 illustrates a cross sectional view of a plastic ball grid array (BGA) packaged RF module 200 of the prior art, such as RF module 100 shown in FIG. 1. As illustrated in FIG. 2, the RFIC 110 is mounted on the lead frame 105 of a package substrate 210. An electrode pad (not shown) of the RFIC 110 is electrically connected to the lead frame inductor 150 via the bonding wire 170. The lead frame inductor 150 is connected to a solder ball 230 through a via 220. The via 220 is formed by punching the package substrate 210 and filling the punched substrate 210 with metal. The plastic BGA packaged RF module 200 includes a mold cap 240 formed of a plastic material. As illustrated, it is apparent that elements of the plastic BGA packaged RF module 200 are spread over a large area, and that heat generated by the RFIC 110 is transported through the RFIC 110 to the lead frame 105 for dissipation. Since the mold cap 240 is not a good conductor of heat, the lead frame 105 acts as a single heat sink for the RFIC 110.
FIG. 3 illustrates a cross sectional view of a thermal enhanced BGA packaged RF module 300 of the prior art, such as RF module 100 shown in FIG. 1. The thermal enhanced BGA packaged RF module 300 is designed to provide a more efficient mechanism for heat dissipation. As illustrated in FIG. 3, the RFIC 110 is mounted on the lead frame 105, and the lead frame 105 is attached to a first surface 312 of a heat sink plate 310. Electrode pads (not shown) of the RFIC 110 are wire bonded to electrode terminals 315 of a multi-PCB layer 320, and connected to solder balls 340 through vias 330 filed with metal in the multi-layered PCB layer 320. A heat transfer gel 350 (also referred to as thermal grease) is deposited on a second surface 314 of the heat sink plate 310. Heat generated by the RFIC 110 is transported from the RFIC 110 to an upper surface 316 of the thermal enhanced BGA packaged RF module 300 via the lead frame 105, the heat sink plate 310, and the heat transfer gel 350. The heat is then dissipated by the upper surface 316.
However, manufacturing process steps in the assembly of the multi-PCB layer 320 are complex, and may lead to low yields. In addition, a multi-PCB layer designed RF module, such as the thermal enhanced BGA packaged RF module 300, is typically voluminous due to the thickness of the multi-PCB layer 320. Furthermore, heat flow is unidirectional, and thus restricted, due to layout and configuration of the RFIC 110, lead frame 105, heat sink plate 310, and thermal grease 350.
In addition to reducing size, another important concern of RF module design engineers is removal of heat generated by the RFIC 110. The RFIC 110 typically includes one or more power amplifiers that generate a large amount of heat that may change transistor parameters and affect RF signal processing operations. It is critical to the stable operation of the RFIC 110 that an RF module package effectively dissipate the heat generated during RF operation. In fact, if heat is not effectively dissipated, electronic components of the RFIC 110 may be damaged and rendered non-operational. Since the plastic BGA packaged RF module 200 (FIG. 2) and the thermal enhanced BGA packaged RF module 300 (FIG. 3) dissipate heat in one direction only, heat transfer rates are poor for these designs.
It is thus desirable to provide a low-profile RF module package having a high heat transfer rate.